(1) Field of the Invention
The present invention relates generally to roller conveyors, and in particular to roller conveyors having a drive system isolated from the rollers, and to a system for detecting the presence and position of objects being conveyed on a roller conveyor and generating a signal in response to the detection of an object.
(2) Description of the Prior Art
Roller conveyors used to convey articles along a given pathway are generally comprised of a plurality of spaced, parallel rollers positioned along and transverse to the pathway. A frame having parallel roller support sections supports the rollers. Each roller has a shaft that is supported at its opposed ends by the frame support sections. The portion of each shaft between the support sections includes a roller body that is used to support the article being conveyed. The roller body may be affixed to the shaft or freely rotatable thereon. The roller body may be continuous along the axis of the roller, or discontinuous, i.e., formed of a plurality of roller body segments or wheels.
A conveyor roller may be a driven roller, i.e., the roller is rotated by a connected drive means, or an idler roller, i.e., the roller is rotated only by the movement of the article across the roller surface. Generally, a plurality of driven rollers are rotated by a single drive means comprised of a rotational power source connected to the plurality of driven rollers either directly or indirectly, by drive connectors, such as belts or chains extending around pulleys or sprockets on the roller shafts. As used herein the term “drive means” is understood to include the power source and the drive connectors.
In many roller conveyor designs, the drive connectors are attached to the rollers within the area where articles are conveyed, e.g., by extending belts around grooves in the roller surfaces. As a result, the articles being conveyed are subject to contamination from the belts that can carry debris into the conveyor pathway. In addition, attachment of belts in this manner makes it difficult to replace or repair the rollers, belts and the drive means to which the belts are attached.
Roller conveyors normally include detectors to detect the presence and position of objects being conveyed on the conveyor. Upon detecting an object, the detector provides input to a counting device or to activate or deactivate power in specific conveyor zone, allowing for pressure-free accumulation of conveyed objects.
Prior art detectors include mechanical contact switches, and non-contact photo-optic or proximity sensors. Both types of prior art detectors have their disadvantages. Mechanical detectors are generally installed between rollers and require spacing of the rollers, impeding smooth flow. Mechanical detectors are also subject to damage by conveyed goods. Photo-optic devices require continual power and need to be wired. Their light sources can also be fooled by ambient light, and are subject to malfunction by dirt and dust. Photo-optic devices are also expensive.
Therefore, there is a continuing need for an improved roller conveyor apparatus having a drive means that is isolated from the rollers and which can be easily attached and replaced. There is also a need for a roller conveyor having an inexpensive detector that will reliably detect the presence of objects on the conveyor and create a signal to another component of the conveyor.